Which of the following medications is the drug of choice for severe preeclampsia?

Labetalol is a adrenoreceptor antagonist which is used in the treatment of severe pre-eclampsia. Although Metoprolol, Alpha methyldopa and Nifedipine are used in the treatment of severe pre-eclampsia, both Hydralazine and Labetalol has emerged as the first line drugs to control the hypeension in severe pre-eclamptic patients. Ref: Dewhurst's Textbook of Obstetrics and Gynaecology By Keith Edmonds; 8th edition, Pages 101-09; Dutta textbook of Obstetrics 6th edition, Pages 221-42